The present invention relates to devices for carrying and balancing centrifuge containers.
Centrifuges are widely used in chemical and biological separation protocols to separate components in liquid samples using centrifugal force. The liquids to be separated are placed into an appropriate container. The container is then placed into a centrifuge rotor which rotates the container at a selected speed.
The weight of containers rotated about an axis must be balanced. Containers of uneven weight create uneven forces as the centrifugal force is applied. This can cause damage to the rotor and/or the container. In addition the separation efficiency degrades under uneven forces. The affect of container imbalance increases with increased rotational speed.
Various fairly complicated and expensive devices have been developed to aid in the balancing of centrifuge containers. For example, U.S. Pat. No. 5,769,775 describes an automated centrifuge which includes a weighing station. The weighing station weighs sample holding racks which are delivered to the weighing station by a robotic arm. The robot arm positions the rack to achieve a balanced arrangement of the rack within a rotor. U.S. Pat. Nos. 5,376,063 and 5,207,634 describe a self-balancing centrifuge apparatus which uses two counter weights. The centrifuge has a plurality of holes for receiving cartridges or other containers. Once the cartridges are loaded into this centrifuge apparatus, the counter weights are moved to a position which will substantially balance the centrifuge. U.S. Pat. No. 4,135,660 describes a pivotal carrier for use with centrifuge rotor. The pivotal carrier contains a plurality of receiving areas for receiving centrifuge containers. The rack can be adjusted to have a balanced weight so that dynamic rotor balance is maintained.
While high precision is required for balancing centrifuge containers under high rotational forces, larger containers spun at slower speeds may tolerate a larger amount of weight difference between containers. Currently centrifuge containers are often balanced through the use of a balance or scale in which containers are weighed and additional liquid is added to opposing containers until the containers are of equal weight and thus in balance when placed on opposing sides within a symmetrical rotor. Such procedure however requires some experimentalist time. In addition the containers then must be loaded into a rack, basket, tray or other transport means and transported to a centrifuge. As an alternative method to balance centrifuge containers some experimentalists simply xe2x80x9ceyeballxe2x80x9d the level of liquid within containers. This practice of visually determining when the liquid level within two containers is equal, is rapid, but prone to error. As container diameter gets larger the error gets larger. The error resulting from improperly balanced containers can cause damage to centrifuge containers and/or rotors as well as detract from centrifuge separation efficiency.
It is the object of the invention to provide a centrifuge labware rack which can also be employed in balancing the opposing weights of centrifuge containers. Such a rack should be durable, simple and inexpensive to manufacture, adaptable to sterilization and easy to use.
It is a further object of the invention to provide a rack that will expedite the loading and balancing of large capacity (typically greater than 1 liter) centrifuge containers used in high capacity centrifuge rotors.
The above objects have been achieved with a centrifuge labware rack for use in balancing centrifuge containers. The labware rack contains two cages positioned on opposite ends of a rigid beam. Centrally located on the beam is a pivot. In using this rack liquid can be poured into a first container contained within a first of the cages on the balance rack. A second container can be put into the second cage and filled with liquid. When the two containers are of approximate balanced weight the rack will begin to tip on the pivot.
The rack has symmetrical weight on either side of the pivot. The rack has a handle for carrying the containers. The rack may also have side cages or trays for holding the lids of centrifuge containers as the centrifuge container is filled with liquid. A spring clip may be added to the ends of the rack to negate the mass of the rack and aid in balancing the containers.